Blood Composition, Circulation, and Common Diseases
Blood Composition and Function
Blood, a vital red fluid, circulates through blood vessels, transporting essential nutrients and oxygen to cells. It also carries away waste products like carbon dioxide, produced during cellular processes.
Blood consists of plasma and blood cells. These cells originate in the bone marrow and include:
- Red blood cells (erythrocytes): The most abundant blood cells, containing hemoglobin, an iron-rich protein. Hemoglobin binds to oxygen in the lungs and transports it throughout the body.
- White blood cells (leukocytes): Defend the body against infections. Key types include:
- Neutrophils and Monocytes: Destroy invading germs.
- Lymphocytes: Produce antibodies to fight microorganisms and eliminate abnormal or cancerous cells.
- Platelets (thrombocytes): Cell fragments crucial for blood clotting.
Blood Vessels
Blood vessels form a network distributing blood throughout the body. There are three main types:
- Arteries: Carry blood from the heart to organs. Their elastic walls maintain blood pressure.
- Veins: Return blood from organs to the heart.
- Capillaries: Tiny vessels with thin walls where substance exchange occurs between blood and cells.
Exchange of Substances
Arteries branch into arterioles, leading to capillaries. High blood pressure in capillaries forces plasma (containing nutrients and oxygen) to filter into interstitial fluid surrounding cells. This fluid, now carrying waste products, returns to capillaries and venules, which merge into veins, carrying blood back to the heart. Interstitial fluid not returning to capillaries becomes lymph.
The Heart
The heart, a hollow, conical organ located between the lungs in the thoracic cavity, is enclosed by the pericardium. Its walls, composed of myocardium, enable rhythmic contractions.
The heart is divided into two halves, each with an atrium and a ventricle. Valves (tricuspid and mitral) regulate blood flow between atria and ventricles.
Heart Function
The heart cycle consists of systole (contraction) and diastole (relaxation):
- Ventricular diastole: Blood passively fills atria and ventricles.
- Atrial systole: Atria contract, pushing blood into ventricles.
- Ventricular systole: Ventricles contract, pumping blood into arteries.
- Ventricular diastole: Ventricles relax, and the cycle repeats.
Circulation
Blood circulation follows two connected circuits:
- Pulmonary circulation: Between the heart and lungs. Deoxygenated blood is pumped from the right ventricle to the lungs for gas exchange.
- Systemic circulation: Between the heart and the rest of the body. Oxygenated blood is pumped from the left ventricle to deliver oxygen and nutrients, and remove waste.
Common Circulatory System Diseases
- Hypertension: Increased blood pressure in arteries. Lifestyle changes, diet, and exercise are crucial for prevention.
- Varicose veins: Swollen veins due to faulty valves, often in the legs.
- Stroke: Interrupted blood supply to the brain, causing varied symptoms.
- Pulmonary embolism: Blockage of a pulmonary artery, often by a blood clot.
- Aneurysm: A bulge in an artery wall.
- Myocardial infarction (heart attack): Blockage of coronary arteries supplying the heart muscle.
- Coagulation disorders: Problems with blood clotting, such as hemophilia.